Modern mobile communication networks use an EPS (‘Evolved Packet System’) architecture, as defined by the standardization body 3GPP, that is based in particular on the distinction between a signalling channel used only to exchange signalling data between the various devices of the network and a user data transport channel used only to exchange payload data with the mobile terminals connected to the network.
Payload data are thus normally transmitted to a mobile terminal in a transport plane, by way of a data transport channel set up between this mobile terminal and the network entity managing access to the networks external to the mobile network.
FIG. 1 illustrates such a data transport channel, also called ‘Data Radio Bearer’ or ‘EPS Bearer’ in the 3GPP standards. In this figure, this data transport channel is carried by the radio interface Uu linking the mobile terminal UE and a base station eNB in the access network part RAN of the mobile network, and then by the interface S1-U linking the base station eNB to the core network part EPC of the mobile network, as far as the service gateway S-GW and the data gateway P-GW, the latter then being used to receive or transmit the data to another external network EXT, for example the Internet.
With regard to the signalling channel employed in the EPS architecture, said channel is based on a logical channel carried by the radio interface Uu, an interface, termed ‘S1-MME’, linking the base station and a mobility management entity MME situated in the core network part EPC of the mobile network.
With such an architecture, for each terminal, a transport channel is set up only when data are transmitted or received by this terminal, exchanges on the signalling channel being necessary to set up this transport channel before the data transmission and to deactivate it at the end of the data transmission.
The ongoing development of IoT (or ‘Internet of Things’ in English) uses makes it possible to contemplate applications that implement transmissions, by a multitude of simple terminals such as sensors, of very small volumes of data, possibly contained in a single IP packet, in contrast to conventional transmissions of voice, image or video data that involve smartphones.
The EPS architecture outlined above is not suitable for this type of transmission of small volumes of data insofar as, even to transmit a small amount of data contained in a single IP packet, it is still necessary to exchange signalling messages between the terminal and the network in order to restore and then to deactivate the transport channel.
In order to improve the effectiveness of the transportation of small volumes of data, in particular in terms of power consumption of the terminal, a solution specific to this type of use alone, called ‘Infrequent small data transmission using pre-established NAS security’, has been presented in the 3GPP technical report TR 23.720 v1.1.0 (clause 6.2).
This solution is based on the introduction of a network entity specific to the transmission of IoT data (in other words low-volume data), denoted ‘C-SGN’, which enables terminals specifically dedicated to this type of use to exchange low-volume data with a mobile network by encapsulating them in signalling messages exchanged with the C-SGN entity, so as to avoid setting up a transport channel.
Such a solution may be advantageous when a very low volume of data has to be transferred, typically when the data fit into a single IP packet. By contrast, if it turns out that the volume of data to be transferred is greater and becomes large, this solution leads to a multiplication of the signalling messages exchanged, thereby possibly leading to greater occupation of the radio link (and therefore a greater power consumption), which would be the case if a conventional transport channel were used to transmit the data.
Application WO 2013/012759 moreover describes a network architecture in which an SPDS (‘Short Packet Data Service’) server is introduced, this server being able to determine that downlink packets have to be transmitted via a signalling channel rather than via a transport channel. When this is the case, this SPDS server dialogs with the MME mobility management entity of the mobile network in accordance with a specific protocol (termed SPDS-AP) so as to transmit to it the low-volume packets to this entity. The MME entity, receiving such packets, then has to send, to the recipient terminal, a ‘paging’ message that is specially modified in order to inform it of the arrival of this specific type of downlink packet.
This mechanism therefore requires burdensome protocol modifications, be this at the MME entity, so that this entity is able not only to dialog with the SPDS server in accordance with the SPDS-AP protocol but also to modify, on a case-by-case basis, the ‘paging’ messages that it sends to the mobile terminals during a downlink connection, but also at the mobile terminals themselves, so that the latter are able to interpret the modified ‘paging’ messages that the MME entity sends to them when there are downlink packets to be transmitted on a signalling channel.
Furthermore, this mechanism is triggered by the SPDS server upon the arrival of data considered to be low-volume. Now, between the time when the SPDS server begins the dialog with the MME entity in accordance with the SPDS-AP protocol and the time when the terminal UE returns an extended service request in order to obtain the downlink data via a signalling channel, this situation may develop, with for example an influx of additional downlink data invalidating the decision of the SPDS server and making the transmission of all of these downlink data via a data transport channel more appropriate. Even if the SPDS server decides to reverse its selection decision, a certain amount of downlink data will already have been transmitted via a signalling channel set up for this purpose, while it is not the most suitable transmission mode.
At the present time, there is therefore not a device that is capable of flexibly, effectively and easily processing both the transmission of low volumes of data and the transmission of high volumes of data within a mobile network.